Automatic single-acting slack adjuster for brake rod linkage

ABSTRACT

The invention concerns itself with an automatically operative and simple operating slack adjuster arrangement for brake rigging for vehicles, especially railway vehicles. It consists of a tubular-shaped body that is axially guided in a fixed housing and in comparison to this cannot be rotated. The tubular body supports thereon two conical clutch surfaces by which, through the means of the aid nut and the clutch nut, the brake as well as respectively the release travel as well as in working conjunction with the contact that is arranged in the fixed housing, the slack adjusting is transferred to the coaxially unrotatable threaded spindle.

United States Patent Frania et al.

[ 51 Sept. 12,1972

[72] Inventors: Josef Frania, l-lannover; Erhard Lehnert, Dollbergen,Kries Burgdorf, both of Germany [73] Assignee: Westinghouse Bremsen-undApparatebau G.m.b.H., Hannover, Germany [22] Filed: April 8, 1971 [2|]Appl. No.: 132,363

[30] Foreign Application Priority Data Easton 188/59 3,430,739 3/1969Persson et al l 88/202 3,572,475 3/1971 Persson et a] ..188/2023,589,480 6/l97l Axelsson et al ..l88/203 Primary Examiner-Duane A.Reger Attorney-Ralph W. Mclntire, Jr.

[57] ABSTRACT The invention concerns itself with an automaticallyoperative and simple operating slack adjuster arrangement for brakerigging for vehicles, especially railway vehicles. It consists of atubular-shaped body that is axially guided in a fixed housing and incomparison to this cannot be rotated. The tubular body supports thereontwo conical clutch surfaces by which, through the means of the aid nutand the clutch nut, the brake as well as respectively the release travelas well as in working conjunction with the contact that is arranged inthe fixed housing, the slack adjusting is transferred to the coaxiallyunrotatable threaded spindle.

l 1 Claims, 2 Drawing Figures PATENTEDSEP 2 i912 3.690.421

I NVENTOR. JOSEF F RANIA ERHARD LEHNERT ATTORNEY AUTOMATIC SINGLE-ACTINGSLACK ADJUSTER FOR BRAKE ROD LINKAGE The present invention concernsitself with the slack adjuster arrangement of the type which has theclutch nut that is equipped with inside and outside threads whereby itsinner thread is in engagement with the thread on a spindle and its outerthread is in engagement with the inner thread of the aid nut. Both setsof threads are of the non-self-locking type and have the same pitch andthe same direction of rotation.

The purpose of this invention is to shorten the construction or overalllength of the slack adjuster arrangement and to improve itsaccessibility, for an example, for the purpose of activating a returnadjustment arrangement as well as respectively to improve the devicethat indicates the maximum permissible brake shoe wear.

This purpose is solved thereby in accordance with the conditions of theinvention so that the tubular body can be displaced by the means of amember of the brake rigging that is movable relative to the housing.

In the practical manner, the tubular body is linked onto the brake leverthat is pivotally mounted on the housing.

In an additional advantageous design set up of the invention, there isprovided in the practical manner an annular disc that is spring loadedby the means of springs that are arcuately arranged in a distributedmanner around the circumference of the disc which is provided with aclutch surface that is pressed by the springs against a clutch surfaceon the aid nut. This disc is arranged to be movable axially relative tothe thrust body by the .meansof the axially symmetrically arrangedguiding studs subsequent to movement of the studs into contact with astop. However, this disc is guided so that it cannot be rotated, wherebythe axis of the guiding studs lie in the plane in which the longitudinalaxis of the tubular body also lies.

In accordance with an additional characteristic of the invention, thethreaded spindle is guided out of the housing and can be rotated by themeans of an appropriate type tool whereby the threaded spindle isconnected with the bearing piece for an additional member of the brakerigging, through the means of the clutch that is built up in thepractical manner as a spiral jaw clutch, so that it cannot be moved,however, it is connected so that it can be rotated with the overcomingof the coupling.

Therethrough, the return positioning arrangement is simplified.

It is further provided in accordance with the invention that in thepractical manner, on the opposite side of the slack adjuster arrangementof the end of the threaded spindle that is guided out from the housing,there is arranged the control device that is activated by the means ofthe threaded spindle and, which is arranged for the indicating devicethat designates the maximum permissible brake shoe wear, whereby thecontrol device can be activated by the means of the spring loadedactivating stud that can be moved axially in the threaded spindle andwhich can be in an unmovable manner connected to the threaded spindle bythe means of the contact arranged on this when the maximum permissiblebrake shoe wear has been attained. Therefore, a simple and space savingactivation is attained for the device that designates the maximumpermissible brake shoe wear.

A typical design in accordance with the conditions of the invention isillustrated in the drawing in a schematic manner.

In the accompanying drawing:

FIG. 1 shows a lengthwise sectional view of a brake assembly for thedisc brake of a railway vehicle with the automatic slack adjusterarranged in accordance with the invention.

FIG. 2 shows a cross-sectional view through the brake unit taken alongthe line 2-2 in FIG. 1.

The brake assembly shown in FIGS. 1 and 2 shows a housing 1 in which, inaccordance with the present invention, a brake cylinder 2 and a slackadjuster mechanism 3 are disposed with their axes arranged inspaced-apart parallel relationship. A piston rod 4 is provided at itsupper end with screw threads by which it is secured to a brake cylinderpiston 40. The piston rod 4 has formed integral therewith intermediatethe ends thereof a collar 5 that has at its lower end a sphericalsurface against which a corresponding spherical surface formed on atwo-part socket member 6, 6a (FIG. 2) is biased by a spring 12interposed between this socket member and a non-pressure head 12a. Asshown in FIGS. 1 and 2, the piston 4 has formed integral therewith anextending in opposite directions therefrom at a location above thecollar 5, as viewed in FIG. 1, a pair of pins 7 and 7a. The respectiveouter ends of the pins 7 and 7a are disposed in corresponding boresformed in each part of a two-part brake lever 8, 8a adjacent theleft-hand end thereof. The parts 6, 6a of the two-part socket member areintegral with the left-hand end of the respective brake lever parts 8and 8a. Adjacent its respective right-hand end, each lever part 8, 8a isprovided with a bore to enable it to be rockably mounted on acorresponding headed pin 9, 9a carried by the housing 1, as shown inFIG. 2.

The slack adjuster mechanism 3 comprises a tubular body 10 havingsecured, as by screw threads (not shown), to its upper end a pair oftrunnions or pins 11, which extend in opposite directions therefrom andpass through bores provided in each part 8, 8a of the two-part brakelever so that the body 10 is movable vertically, as viewed in FIG. 1, asthis brake lever 8, 8a is rocked about the pins 9, 9a. The lower end ofthe tubular body 10 has integral therewith an inturned flange on whichis formed two oppositely inclined internal conical-shaped clutch facesor surfaces 13 and 14. As shown in FIG. 1, a nut member 16, adjacent itslower end, is provided with a first external conical-shaped clutch face17 having the same angle of inclination as the internal clutch face 13and with a second external conical-shaped clutch face 18. A hollowclutchnut member 15 has integral therewith at its lower end an outturnedflange on which is formed a third external conical-shaped clutch face15a having the same angle of inclination as the internal clutch face 14.An annular member or disc 19 is provided with an internal conicalshapedclutch face 19a that has the same angle of inclination as the externalclutch face 18 on the nut member 16.

The annular member 19 is provided with a plurality of arcuately-spacedbottomed bores 19b. interposed between the bottom of each bottomed bore19b and an annular member 190 is one of a plurality of springs 16, andinterposed between the annular member 190 and an outturned flange 16aintegral with the upper end of the nut member 16 is a plurality ofarcuately arranged balls which constitute a ball bearing. Accordingly,it is apparent from FIG. 1 that the springs 26 are normally effective tobias the internal clutch face 19a on the annular disc 19 into clutchingcontact with the external clutch face 18 on the nut member 16.

The annular disc 19 can be axially moved, that is vertically in FIG. 2,with respect to the tubular body 10. However, it cannot be rotated withrespect to body since a pair of guide pins 20, 20a that are integralwith and extend from the low side of annular disc 19 pass throughcorresponding bores 21, 21a provided in the inturned flange that isintegral with body 10.

The lower end of the housing 1 has formed integral therewith an inturnedflange la that is provided with internal screw threads whereby a contactring or stop member 22 having external screw threads can be screwed intoor out of the housing 1. The stop member 22 is provided with a pair ofinternally threaded bottomed bores for receiving a pair of cap screws44, 440 that secure an end cover 44b to the housing 1.

The clutch nut member is provided with an internal non-self-locking typeof screw thread which has screw-threaded engagement with an externalnon-selflocking screw thread formed on a spindle or brake rod 23, thelower end of which extends to the exterior of the housing 1 and isprovided with a hexagonal head 24 for receiving a wrench by which thespindle 23 can be rotated to let out slack when installing new brakeshoes on the railway car.

The clutch nut member 15 is also provided with an externalnon-self-locking type of screw thread which has screw-threadedengagement with an internal nonself-locking screw thread formed in thenut member 16. All of the above-mentioned non-self-locking types ofscrew threads have the same pitch and it will be understood areright-hand threads.

The upper end of the clutch nut member 15 is provided with an outturnedflange 15b between which and an inverted cup-shaped-member 25 having anoutside diameter substantially less than the inside diameter of thetubular body 10 are disposed a plurality of balls 25a which constitute aball bearing. Thus, a definite limited amount of play is providedbetween the cup-shaped member 25 and the tubular body 10 as indicated at25b.

As shown in FIG.' 1, a spring 27 is interposed between the cup-shapedmember 25 and the annular disc 19. This spring 27 in cooperation withthe plurality of springs 26 is effective to normally bias all threepairs of clutch faces 14 and 15a, 13 and 17, and 19a and 18, intoclutching contact one with the other.

While the brakes are released and the parts of the slack adjustermechanism 3 occupy the position shown in the drawing, the clearance Ashown in FIG. 1 between the contact ring or stop 22 and the guide pins20, a corresponds to the normal clearance between the brake shoes and amember to be braked, such as a brake disc. This clearance can be easilyadjusted or changed by adjusting the contact ring or stop 22 relative tothe inturned flange 1a that is integral with housing 1.

A cup-like bearing piece 28, which is arranged coaxially about thespindle 23 and constitutes the second part of a two-part brake rod, hasa ball-like guide ring 29 interposed between it and thehereinbefore-mentioned end cover 44b through which this bearing piece 28extends to the exterior thereof.

A spiral-jaw clutch 33 is provided between the spindle 23 and thebearing piece 28, one set of jaws 30 being provided on the spindle 23and the other set of jaws 31 being provided on the bearing piece 28.These jaws are normally biased into engagement one set with the other bya spring 32, the strength of which exceeds the strength of thehereinbefore-mentioned spring 12.

The bearing piece 28 has formed integral therewith a pair of trunnions28a and 28b on which is pivotally mounted one end of a brake lever 28c.

The upper end of the housing 1 is closed by a cover 10 to which acontrol valve 34 is secured by any suitable means (not shown). Thiscontrol valve 34 serves to control the supply and release of fluid underpressure to a pneumatically operated brake shoe wear-indicating device(not shown) and comprises an annular disc valve 35 normally springbiased against an exhaust valve seat 37 formed on a valve stem 36 andunseated from a supply valve seat 38.

A delivery passageway 39 in the control valve 34 is connected by a pipe(not shown) to the wear-indicating device and a supply passageway 40 isconnected by a pipe (not shown) to a source of fluid under pressure. Anexhaust passageway 41 is open to atmosphere.

A spring-biased operating stem 42 is pressed against the lower end ofthe valve stem 36. This operating stem 42 is carried in the spindle 23which is provided with a projection or stop 43 that limits the upwardmovement of the operating stem 42 relative to the spindle 23.

When a brake application is effected, fluid under pressure is suppliedto the upper side of the piston 4a via a passageway 2a which isconnected by a pipe (not shown) to the brake cylinder port of the usualbrake control valve provided on each railway car. This fluid underpressure is effective to move the piston 4a and piston rod 4 downwardagainst the yielding resistance of spring 12 to rock, via the pins 7,7a, the two-part brake lever 8, 8a about the pins 9, (FIG. 2). Thisrocking of the lever 8, 8a is effective, via pins 11 and 11a, to movethe tubular body 10 downward. It can be seen from FIG. 1 that the slackadjuster mechanism 3 is likewise moved downward. Consequently, thespindle 23, which is connected by the spiral-jaw clutch 33 to thebearing piece 28, moves downward to effect rocking of the brake lever280 in the direction to force the brake shoes against the brake disc tocause a brake application.

Assume proper or normal brake shoe clearance between the braking surfaceof the brake shoes and the brake disc, which distance may be, asaforestated, the distance A shown in FIG. 1. Therefore, the brakingsurface of the brake shoes is moved into contact with the brakingsurface of the brake disc substantially at the same time as the guidepins 20, 20a abut the stop 22.

When it is desired to release the brake application, the fluid underpressure supplied to the upper face of the piston 4a is vented in theusual manner to atmosphere through the passageway 20 and the brakecontrol valve of the car brake system, whereupon the force of the spring12 acting on the non-pressure head 12a and the two-part socket member 6,6a returns the piston 4a, lever 8, 8a and the slack adjuster mechanism 3to the position shown in the drawing.

Assume that a brake application has been effected in the mannerhereinbefore described, and that, during the brake application, thebraking surface of the brake shoes wears away. As this wearing away ofthe braking surface of the brake shoes occurs, the fluid under pressureacting on the piston 4a is effective to cause further counterclockwiserocking, as viewed in FIG. 1, of the brake lever 8, 8a to thereby effectdownward movement of tubular body 10, which movement is transmitted viaclutch faces 14 and 15a, clutch nut member 15, spindle 23, spiral-jawclutch 33, bearing piece 28 and brake lever 28c to maintain the brakingsurface of the brake shoes in braking contact with the braking surfaceof the brake disc and thus the braking force on this disc.

It will be remembered that at the time the braking surface of the brakeshoes was moved into contact with the braking surface of the brake disc,the guide pins 20, 20a, which are integral with annular disc 19, weremoved into abutting relationship with the upper side of stop 22.Therefore, it will be apparent from FIG. 1 that, as the tubular body 10,clutch nut member 15, nut member 16, spindle 23 and bearing piece 28 aremoved downward in the manner explained above in response to the wearingaway of the braking surface of the brake shoes, the external clutch face18 on the nut member 16 is moved downward out of clutching contact withthe internal clutch face 190 on the now stationary annular member 19.Subsequent to movement of the external clutch face 18 on nut member 16out of clutching contact with the internal clutch face 19a on nowstationary annular member 19, the spring 27 exerts a force via thecup-shaped member 25, balls 25a and flange 15b on the clutch nut member15 which acts in an upward direction, as viewed in FIG. 1. This force istransmitted via external clutch face 15a on clutch nut member 15 to theinternal clutch face 14 formed on the tubular body which is being movedin a downward direction by the brake lever 8, 8a.

It will be noted from FIG. 1 that the springs 26 transmit a force to thenut member 16 via annular member 19c, outturned flange 16a and the ballstherebetween, which force acts in an upward direction as viewed in FIG.1, on the nut member 16. Therefore, as the tubular member 10 is moveddownward by the brake lever 8, 8a the internal clutch face 13 on theintumed flange that is integral with the tubular member 10 is moved outof clutching contact with the external clutch face 17 on the nut member16.

In view of the above, it is apparent that as the tubular member 10,clutch nut member 15, spindle 23, spiral jaw clutch 33 and bearing piece28 are moved downward to maintain the braking surface of the brake shoesin contact with the braking surface of the brake disc as the brake shoeswear away, the springs 26 are effective to cause the nut member 16 torotate on the clutch nut member to thereby increase the effective lengthof the spindle 23 as the brake shoes wear away.

Now let it be supposed that, subsequent to this wearing away of thebraking surface of the brake shoes released by venting fluid underpressure from the upper face of the piston 4a to atmosphere in the usualmanner hereinbefore described.

As the brake lever 8, 8a is now rocked clockwise, as viewed in FIG. 1,by the spring 12 in response to the venting of fluid under pressure fromthe upper face of while the brake application was in effect, the brakesare piston 4a, the tubular member 10 is moved upward to cause upwardmovement of bearing piece 28, spindle 23 and clutch nut member 15, sothat the internal clutch face 13 on the intumed flange integral with thetubular body 10 is moved into clutching contact with the external clutchface 17 on the nut member 16, it being understood that thehereinbefore-mentioned rotation of the nut member 16 relative to theclutch nut member 15 by the springs 26 continued until the externalclutch face 18 on the nut member 16 was moved into clutching contactwith the internal clutch face 19a on the stationary annular member 19.The continued clockwise rocking of the brake lever 8, 8a subsequent toexternal clutch face 18 on the nut member 16 moving into clutchingcontact with the internal clutch face 19a on the annular member 19 willmove this member 19 and the guide pins 20, 29 upward relative to thestop 22 until this member 19 andvthe tubular body 10 are returned to theposition shown in FIG. 1.

The operation of the control valve 34 and the brake shoe wear-indicatingdevice connected thereto will now be described.

As long as the wear of the brake shoes is less than a chosen amount, thevalve stem 36 is held in the position shown by the operating stem 42 anda spring 43a interposed between the stem 42 and the spindle 23. In thisposition of the valve stem 36, the disc valve 35 is seated on exhaustvalve seat 37 and unseated from supply valve seat 38 so that fluid flowsfrom the source of fluid under pressure to the wear-indicating devicevia passageways 40 and 39 and the corresponding pipes (not shown) sothat this device is maintained in the position to indicate that brakeshoe wear is less than a chosen amount.

When the maximum permissible brake shoe wear has occurred, the slackadjuster mechanism 3 has operated to rotate the spindle 23 and move itdownward, as viewed in FIG. 1, far enough for the flange on the lowerend of the stem 42 to abut the stop 43 and thereafter move the stem 42downward far enough for the springs to seat valve 35 on supply valveseat 38 and move exhaust valve seat 37 downward away from valve 35. Thewear-indicating device is now connected to atmosphere via pipe andcorresponding passageway 39, the port in disc valve 35 and exhaustpassageway 40. When fluid under pressure is thus vented from thewear-indicating device, it moves to the position to indicate that themaximum permissible brake shoe wear has occurred.

In order to return the spindle 23 to its original position wheninstalling new brake shoes, this spindle 23 is manually rotated by meansof a wrench that may be placed on the hexagonal head 24, it beingunderstood that the jaws of spiral-jaw clutch 33 slide one over theother against the yielding resistance of the spring 32 as spindle 23 isrotated by the wrench. By virtue of this slipping of the jaws of thespiral-jaw clutch 33, the bearing piece 28 is held secured against orprevented from rotating by means of the brake lever 28 which isconnected thereto by the trunnions 28a and 28b.

Since the spring 32 is stronger than the spring 12, this insures thatwhen a brake release is effected, the spiraljaw coupling 33 maintainsthe connection between the spindle 23 and the bearing piece 28.

The present invention, which constitutes a slack adjuster mechanismarranged in parallel spaced-apart relation to a brake cylinder, providesa short and compact brake assembly enclosed within a single casing. Thebiasing of the internal clutch face 1921 on the annular member 19 intoclutching contact with the external clutch face 18 on the nut member 16by means of the plurality of springs 26 arranged arcuately about theannular member 19 rather than by a single spring arranged coaxial withthe member 1? enables the overall length of the slack adjuster mechanismto be shorter than it would otherwise be. The slack adjuster mechanismis easily accessible from the outside, as shown in FIG. 1. The hexagonalhead 24 for manually letting out slack is provided at the lower end ofthe slack adjuster mechanism and the control valve 34 for the brake shoewear-indicating device at the upper end.

The construction and operation of the manual slack let-out mechanism isvery simple since only the spindle 23 is rotated in a reverse directionrelative to the other parts of the slack adjuster mechanism.

Having now described the invention, what we claim as new and desire tosecure by Letters Patent is:

1. A brake assembly for applying a braking force to a member to bebraked, said assembly having a casing provided with a brake cylindertherein, and a piston operative in said brake cylinder and movable inopposite directions responsively to supply and release of fluid underpressure to and from a chamber at one side thereof, wherein theimprovement comprises:

a. an operating lever pivotally mounted adjacent one end on'said casingand operatively connected adjacent its opposite end to said piston forrocking movement by said piston,

b. a two-part brake rod movably supported on said casing for axialmovement substantially in a straight line, one end of said rod having apivotal connection with a brake lever, and

c. a slack adjuster mechanism interposed between and operativelyconnected to said operating lever and one part of said two-part brakerod, said slack adjuster mechanism comprising:

i. a triple clutch mechanism having:

1. a tubular member pivotally connected adjacent one end to saidoperating lever intermediate the ends thereof and having at its oppositeend an inturned flange on which is provided a pair of axially spacedclutch faces,

2. a first nut member coaxially related to said tubular member andhaving a pair of axially spaced clutch faces, one of which cooperateswith one of said clutch faces on said inturned flange,

3. an annular member disposed in and having guide means for axialmovement with respect to said tubular member and a clutch face whichcooperates with the other of said clutch faces on said first nut member,and

4. a clutch nut member having at one end an outturned flange on which isprovided a clutch face which cooperates with the other of said clutchfaces on said inturned flange, and having an external and an internalnon-selflocking screw thread of different diameters,

5. said first nut member and one part of said two-part brake rod havingrespectively internal and external non-self-locking screw threads ofdifferent diameter, whereby said first nut member is rotatably mountedon said clutch nut member, and said clutch nut member is rotatablymounted on said one part of said brake rod,

ii. a stop on said casing disposed in the pathway of said guide means,

iii. a plurality of spring seats carried by said annular member,

iv. a pair of spring seats,

v. a plurality of springs, each interposed between one of said springseats carried by said annular member and one of said pair of springseats,

vi. another spring interposed between said annular member and the otherof said pair of spring seats,

vii. a pair of bearings disposed respectively between one of said pairof spring seats and said first nut member, and between the other of saidpair or spring seats and said clutch nut member,

viii. said plurality of springs being effective via one of said pair ofbearings to cause rotation of said first nut member relative to saidclutch nut member, while said pair of axially spaced clutch faces onsaid first nut member are disengaged, in response to further rocking ofsaid operating lever in one direction subsequent to said guide meanscontacting said stop, until said other clutch face on said first nutmember reengages said clutch face on said annular member, and

ix. said another spring being effective via the other of said pair ofbearings to cause rotation of said clutch nut member relative to saidone part of said two-part brake rod while said clutch face on saidclutch nut member is disengaged from said other clutch face on saidinturned flange until said clutch faces reengage to increase theeffective length of said one part of said two-part brake rod as saidbrake shoes wear.

2. A brake assembly, as recited in claim 1, further characterized inthat said operating lever comprises two parts, each part being pivotallymounted adjacent one end on said casing and operatively connectedadjacent its opposite end to said piston for simultaneous rockingmovement by said piston.

3. A brake assembly, as recited in claim 1, further characterized inthat said operating lever comprises two parts, and said tubular memberis pivotally connected by a trunnion to said two parts of said operatinglever intermediate the ends of each of said parts whereby rocking ofsaid lever effects longitudinal displacement of said tubular memberrelative to said casmg.

4. A brake assembly, as recited in claim 1, further characterized inthat said plurality of spring seats carried by said annular member arearcuately arranged in spaced-apart relation on one side thereof, and theaxes of said guide means and the axis of said tubular member lie in acommon plane.

5. A brake assembly, as recited in claim 1, further characterized by ascrew-threaded connection between said stop and said casing whereby saidstop is adjustable relative to said casing.

6. A brake assembly, as recited in claim 1, further characterized inthat said one part of said two-part brake rod extends through the otherpart to the exterior of said casing for receiving a tool to effectmanual rotation thereof. I

7. A brake assembly, as recited in claim 1, further characterized inthat the two parts of said brake rod are connected by a spiral-jawclutch whereby one part may be rotated in only one direction relative tothe other part.

8. A brake assembly, as recited in claim 1, further characterized inthat a ball-type guide member is interposed between said other part ofsaid two-part brake rod and said casing.

9. A brake assembly, as recited in claim 1, further characterized by acontrol valve carried on said casing for controlling operation of abrake shoe wear-indicating device, and by means carried in and operatedby one part of said two-part brake rod for effecting operation of saidcontrol valve.

10. A brake assembly, as recited in claim 2, further characterized by apiston rod carried by said piston and a ball and socket means connectingsaid piston rod to said two-part operating lever, said ball and socketmeans comprising:

a. a ball member carried by said piston rod, and

b. a two-part socket member, said two parts being carried respectivelyby said two parts of said operating lever.

11. A brake assembly, as recited in claim 7, further characterized bybiasing means for normally effecting operation of said spiral-jaw clutchto provide a yieldable connection between said two parts of said brakerod.

1. A brake assembly for applying a braking force to a member to bebraked, said assembly having a casing provided with a brake cylindertherein, and a piston operative in said brake cylinder and movable inopposite directions responsively to supply and release of fluid underpressure to and from a chamber at one side thereof, wherein theimprovement comprises: a. an operating lever pivotally mounted adjacentone end on said casing and operatively connected adjacent its oppositeend to said piston for rocking movement by said piston, b. a two-partbrake rod movably supported on said casing for axial movementsubstantially in a straight line, one end of said rod having a pivotalconnection with a brake lever, and c. a slack adjuster mechanisminterposed between and operatively connected to said operating lever andone part of said two-part brake rod, said slack adjuster mechanismcompriSing: i. a triple clutch mechanism having:
 1. a tubular memberpivotally connected adjacent one end to said operating leverintermediate the ends thereof and having at its opposite end an inturnedflange on which is provided a pair of axially spaced clutch faces,
 2. afirst nut member coaxially related to said tubular member and having apair of axially spaced clutch faces, one of which cooperates with one ofsaid clutch faces on said inturned flange,
 3. an annular member disposedin and having guide means for axial movement with respect to saidtubular member and a clutch face which cooperates with the other of saidclutch faces on said first nut member, and
 4. a clutch nut member havingat one end an outturned flange on which is provided a clutch face whichcooperates with the other of said clutch faces on said inturned flange,and having an external and an internal non-self-locking screw thread ofdifferent diameters,
 5. said first nut member and one part of saidtwo-part brake rod having respectively internal and externalnon-selflocking screw threads of different diameter, whereby said firstnut member is rotatably mounted on said clutch nut member, and saidclutch nut member is rotatably mounted on said one part of said brakerod, ii. a stop on said casing disposed in the pathway of said guidemeans, iii. a plurality of spring seats carried by said annular member,iv. a pair of spring seats, v. a plurality of springs, each interposedbetween one of said spring seats carried by said annular member and oneof said pair of spring seats, vi. another spring interposed between saidannular member and the other of said pair of spring seats, vii. a pairof bearings disposed respectively between one of said pair of springseats and said first nut member, and between the other of said pair orspring seats and said clutch nut member, viii. said plurality of springsbeing effective via one of said pair of bearings to cause rotation ofsaid first nut member relative to said clutch nut member, while saidpair of axially spaced clutch faces on said first nut member aredisengaged, in response to further rocking of said operating lever inone direction subsequent to said guide means contacting said stop, untilsaid other clutch face on said first nut member reengages said clutchface on said annular member, and ix. said another spring being effectivevia the other of said pair of bearings to cause rotation of said clutchnut member relative to said one part of said two-part brake rod whilesaid clutch face on said clutch nut member is disengaged from said otherclutch face on said inturned flange until said clutch faces reengage toincrease the effective length of said one part of said two-part brakerod as said brake shoes wear.
 2. a first nut member coaxially related tosaid tubular member and having a pair of axially spaced clutch faces,one of which cooperates with one of said clutch faces on said inturnedflange,
 2. A brake assembly, as recited in claim 1, furthercharacterized in that said operating lever comprises two parts, eachpart being pivotally mounted adjacent one end on said casing andoperatively connected adjacent its opposite end to said piston forsimultaneous rocking movement by said piston.
 3. A brake assembly, asrecited in claim 1, further characterized in that said operating levercomprises two parts, and said tubular member is pivotally connected by atrunnion to said two parts of said operating lever intermediate the endsof each of said parts whereby rocking of said lever effects longitudinaldisplacement of said tubular member relative to said casing.
 3. anannular member disposed in and having guide means for axial movementwith respect to said tubular member and a clutch face which cooperateswith the other of said clutch faces on said first nut member, and
 4. aclutch nut member having at one end an outturned flange on which isprovided a clutch face which cooperates with the other of said clutchfaces on said inturned flange, and having an external and an internalnon-self-locking screw thread of different diameters,
 4. A brakeassembly, as recited in claim 1, further characterized in that saidplurality of spring seats carried by said annular member are arcuatelyarranged in spaced-apart relation on one side thereof, and the axes ofsaid guide means and the axis of said tubular member lie in a commonplane.
 5. A brake assembly, as recited in claim 1, further characterizedby a screw-threaded connection between said stop and said casing wherebysaid stop is adjustable relative to said casing.
 5. said first nutmember and one part of said two-part brake rod having respectivelyinternal and external non-self-locking screw threads of differentdiameter, whereby said first nut member is rotatably mounted on saidclutch nut member, and said clutch nut member is rotatably mounted onsaid one part of said brake rod, ii. a stop on said casing disposed inthe pathway of said guide means, iii. a plurality of spring seatscarried by said annular member, iv. a pair of spring seats, v. aplurality of springs, each interposed between one of said spring seatscarried by said annular member and one of said pair of spring seats, vi.another spring interposed between said annular member and the other ofsaid pair of spring seats, vii. a pair of bearings disposed respectivelybetween one of said pair of spring seats and said first nut member, andbetween the other of said pair or spring seats and said clutch nutmember, viii. said plurality of springs being effective via one of saidpair of bearings to cause rotation of said first nut member relative tosaid clutch nut member, while said pair of axially spaced clutch faceson said first nut member are disengaged, in response to further rockingof said operating lever in one direction subsequent to said guide meanscontacting said stop, until said other clutch face on said first nutmember reengages said clutch face on said annular member, and ix. saidanother spring being effective via the other of said pair of bearings tocause rotation of said clutch nut member relative to said one part ofsaid two-part brake rod while said clutch face on said clutch nut memberis disengaged from said other clutch face on said inturned flange untilsaid clutch faces reengage to increase the effective length of said onepart of said two-part brake rod as said brake shoes wear.
 6. A brakeassembly, as recited in claim 1, further characterized in that said onepart of said two-part brake rod extends through the other part to theexterior of said casing for receiving a tool to effect manual rotationthereof.
 7. A brake assembly, as recited in claim 1, furthercharacterized in that the two parts of said brake rod are connected by aspiral-jaw clutch whereby one part may be rotated in only one directionrelative to the other part.
 8. A brake assembly, as recited in claim 1,further characterized in that a ball-type guide member is interposedbetween said other part of said two-part brake rod and said casing.
 9. Abrake assembly, as recited in claim 1, further characterized by acontrol valve carried on said casing for controlling operation of abrake shoe wear-indicating device, and by means carried in and operatedby one part of said two-part brake rod for effecting operation of saidcontrol valve.
 10. A brake assembly, as recited in claim 2, furthercharacterized by a piston rod carried by said piston and a ball andsocket means connecting said piston rod to said two-part operatinglever, said ball and socket means comprising: a. a ball member carriedby said piston rod, and b. a two-part socket member, said two partsbeing carried respectively by said two parts of said operating lever.11. A brake assembly, as recited in claim 7, further characterized bybiasing means for normally effecting operation of said spiral-jaw clutchto provide a yieldable connection between said two parts of said brakerod.